Electrophoretic method of applying a low friction coating



2,826,542 ELECTROPHORETIC METHOD OF APPLYING A LOW FRICTION COATINGJames J. Sliyne, Arlington, N. 1., and Howard G. Scheible,

Middle Village, N. Y., assignors to Vitro Corporation of America,Verona, N. I.

No Drawing; Application June 16, 1954 Serial No. 437,286 7 Claims. (Cl.204- 181) Our invention relates to lubricated or low friction metalstructures and methods for producing the same.

Certain inorganic compounds, i. e., the sulphides, disulphides,selenides and tellurides of such metals as molybdenumflungsten, titaniumand uranium are characterized by a laminated or plate-like crystalstructure in which the metallic atomsare attached to each other in asingle common plane while the non-metallic atoms are attached to themetallic atoms to form layers on both sides of this plane. Thenon-metallic atoms in each of the several crystals thus formed have verylittle attraction for each other so that these crystals wil slip readilywith response to each other under the action of low shearing forces.Moreover, the non-metallic atoms have an afiinity for adjacent metalsurfaces so that the crystals attached to such surfaces will exhibitvery strong resistance to the action of forces normal to the directionof shear. Consequently, these compounds have excellent lubricatingproperties and also have excellent anti-seizing properties. The termLaminated Metallic Lubricating Agents has been selected to denotecompounds of this class.

In application S. N. 404,796, filed January 18, 1954, by F. Fahnoe andJ. I. Shyne, a process is disclosed for depositing a solid lubricantcoating on the surface of a base member. In this method a mixture ofreducible metallic compounds and laminated metallic lubricating agentsare electrophoretically codeposited on the surface of a base metallicmember and the reducible compound is subsequently reduced to metal toform a sintered metal matrix which is bonded to the base member andwhich in turn entraps an bonds the lubricating agent or agents to thestructure to form a lubricant coating. Metals which are capable offorming such a bonding matrix as disclosed in said application includecopper, tin, zinc, chromium, nickel and silver. The relative proportionsof the reducible compounds and lubricating agents are such that thelubricant adheres uniformly tothe structure until the structure issubjected to a metal-Working operation. During. this operation thecoating, while supplying the desired amount of lubricating, isprogressively worn away or stripped from the structure. The termSacrificial Layer has been selected to denote this type of coatmg.

States Patent In another application S. N. 402,402, filed January 5,

1954, by F. Fahnoe and J. J. Shyne we disclosed a process for depositinga low friction coating on the surface of a base member. This process issimilar to that of S. N. 404,796 in that a mixture of reducible metalcompounds and friction modifying agents having low coefficients offriction are electrophoretically codeposited on the surface of a basemetal member and the reducible compound reduced to metal to bond thefriction modifying agents to the base member. Metals which are capableof forming a bonding matrix as disclosed in said patent applicationinclude nickel, copper, iron, chromium and alloys as well as tin, lead,silver and alloys thereof. (These low friction modifying agents includeas a sub-class all laminated metallic lubricating agents and furtherinclude substances, for example, graphite, which have low frictionproperties and which re not 'ncluded in this subclass). In this process,however, the low friction coat- 0 which is formed ing thus formed ispermanent and is not appreciably worn ice ing operation.

In ofd'er to form a sacrificial layer the percentage content by weightof reducible metal compound must fall within the range %80%; in order toform a permanent coating this percentage content must fall within therange %'95%.

In our work on both of these processes we have dis covered that whenelectrophoretically deposited coatings composed of reducible metallicoxides and laminated metallic lubricating agents of the sulphide ordisulphide type are deposited on a metal base member or metal substrate,and when the subsequeni reduction operation is carried out in a hydrogenatmosphere at high temperatures, both the compound and a portion of thelaminated metallic lubricating agent used are also reduced, and thelubricating or low friction properties of the resultant coating, whilestill evident, are reduced in efiectiven'ess.

Accordingly, it is an object of the present invention to provideimproved processes of the character indicated in which the lubricatingproperties are not impaired under the above conditions.

Still a further object is to provide an improved process of thecharacter indicated wherein both the reducible of the characterindicated wherein the reducible metallic compounds are mixtures ofoxides and sulphides or disulphides and the reaction is carried out inan inert atmosphere.

In one form of our invention a mixture of easily reducible metalliccompounds of the sulphide or disulphide type and laminated metalliclubricating agents of the sulphide or disulphide type areelectrophoretically codeposited on the surface of a base metal. Underthe conditions indicated below, the chemical activity of the metalliccompound selected substantially exceeds the activity of the lubricatingagent. Consequently, when the coated member is heated in a hydrogenatmosphere, hydrogen sulphide gas is formed, and the metallic compoundis reduced to metal. The presence of the hydrogen sulphide gas preventsany appreciable reduction of the laminated lubricating agent to itsmetal. Consequently, the reduced metallic compound forms a sinteredmetal matrix which is bonded to the base member and which in turnentraps and bonds the unreduced lubricating agent particles to themember to form'the desired lubricant coating.

In another form of our invention, a mixture of metallic oxides andmetallic sulphides or disulphides is electrophoretically codepositedwith at least one laminated metallic lubricating agent of the sulphideor disulphide type on the surface of a base metal or substrate. Underthe conditions indicated below, the chemical activity of these materialsis such that the metallic oxides and sulphides or disulphidespreferentially react with each other rather than with the lubricatingagent. The coated member is then heated in an inert atmosphere. Thelubricatine agent is not reduced but both the metallic oxide and themetallic sulphide or disulphide used are reduced to metal, and sulphurdioxide gas is formed. The metal by interaction between the metallicsulphide or disulphide and the metallic oxide, as in the structures andprocesses referred to above, produces a' thus causing migration of thesuspended particles toward one of the electrodes, and producing adeposit of an adherent coating on that electrode. Exceptional uniformityof coatingthickness and compactness (with a relatively high coatingdensity) are obtained as compared with dipping, spraying, brushing andother more conventional methods of application. Irregularly shapedobjects can be coated with excellent uniformity and reproducibility ofcoating. A complete description of the electrophoretic process will befound in copending application S. N. 388,119, filed October 26, 1953, byF. Fahnoe and J. J. Shyne.

The following examples set forth certain well-defined instances of theapplication of this invention. They are, however, not to be consideredas limitations thereof since many modifications can be made withoutdeparting from the spirit and scope of this invention.

Example I duced to copper in the form of a sintered matrix bonded bycodiffusion to the surface of the sheet. The molybdenum disulphideparticles substantially unaltered were found to be entrapped within thepores of the matrix.

Example [I A coating .010" thick containing 22% by weight of molybdenumdisulphide particles and 77 by weight of stoichiometric quantities ofcopper(ous) oxide and copper(ous) sulphide were electrolyticallydeposited on a stainless steel substrate in the manner outlined asbefore. The sheet was then fired in a helium atmosphere at a temperatureof 1400 F. for a period of 30 seconds. The formation of sulphur dioxidegas was observed during this period. Subsequent cross-sectional analysisestablished that both the copper oxide and copper sulphide had beenreduced to copper in the form of a sintered matrix bonded by codifiusionto the surface of the sheet. The molybdenum disulphide particles werefound to be entrapped within the pores of the copper matrix.

While we have shown, described and pointed out fundamental novelfeatures of the invention as applied to preferred embodiments, it willbe understood that various omissions, substitutions and changes in theform and details from the spirit of the invention. It is our intention,therefore, to be limited only as indicated by the scope of the claimswhich follow.

7 We claim:

1. A method of applying a low friction coating to the surface of a metalsubstrate which comprises the steps of electrophoretically depositingout of a liquid medium upon the surface of said substrate a coatingformed from a mixture of between 30%5% by weight of at least onelaminated metallic lubricating agent selected from the class consistingof sulfides and disulfides of molybdenum, tungsten, titanium and uraniumand between 70%95% by weight of at least one reducible metallic compound4 other than said metallic lubricating agent selected from the classconsisting of sulfides and disulfides, said compound being reducible toform a metallic matrix bonded to said metal substrate at a temperatureat which the vmetallic lubricating agent doesnot undergo substantialreduction; and heating said coated metal substrate in a reducingatmosphere at a temperature high enough to reduce said metallic compoundto the metal but below the temperature at which substantialdecomposition of said lubricating agent takes place until said metalliccompound is reduced to metal thereby to form a metallic matrix which isbonded to said surface of said metal substrate and which entraps andbonds said solid lubricant to said substrate.

2. The method as set forth in claim 1 wherein the metallic compound iscopper sulfide. 3. The method of applying a low friction coating tothe'surface of a metal substrate which comprises the steps ofelectrophoretically depositing out of a liquid medium upon the surfaceof said substrate a coating formed from a mixture of between 30%-5% byweight of at least one laminated metallic lubricating agent selectedfrom the class consisting of sulfides and disulfides of molybdenum,tungsten, titanium and uranium, and between %95% by weight of tworeducible metallic compounds other than the metallic lubricating agent,one of said compounds being an oxide and the other being selected fromthe class consisting of sulfides and disulfides, said compounds beingpresent in stoichiometric quantities to form the corresponding metal andsulphur dioxide and being reducible in the presence of each other toform a metallic matrix bonded to said metal substrate at temperatures atwhich the metallic lubricating agent does not undergo substantialreduction; and heating said coated metal substrate in an inertatmosphere at a temperature high enough to decompose said metalliccompounds to the metals and sulphur dioxide but below the temperature atwhich a substantial decomposition of said lubricating agent takes placeuntil sulphur dioxide gas is formed and both of said compounds arereduced to metal, thereby to form a metallic matrix which is bonded tosaid surface of said metal substrate and which entraps and bonds saidlubricant to said substrate.

4. The method as set forth in claim 3 wherein said metallic compoundsare both compounds of the same metal. a

5. The method set forth in claim 4 wherein said same metal iscopper.

6. The method of applying a low friction coating to the surface of ametal whichcomprises the steps of electrophoretically depositing out ofliquid media upon the surface of said metal a coating formed from amixture of between 70%95% by weight of cuprous oxide and cuprous sulfidepresent in stoichiometric quantities to form metallic copper and sulphurdioxide and between 30%5% by weight of molybdenum disulfide; and heatingsaid coated metal in an inert atmosphere until sulphur dioxide gas isformed and both of said cuprous compounds are reduced to metallic copperin the form of a matrix bonded to said metal, said molybdenum disulfidebeing substantially unaffected by said reduction whereby said molybdenumdisulfide is entrapped within the pores of said matrix.

7. The method as set forth in claim 6 wherein said atmosphere is ahelium atmosphere.

References Cited in the file of this patent UNITED STATES PATENTSSociety, vol. 54 (1928), pp. 315 to 321.

1. A METHOD OF APPLYING A LOW FRICTION COATING TO THE SURFACE OF A METALSUBSTRATE WHICH COMPRISES THE STEPS OF ELECTROPHORETICALLY DEPOSITINGOUT OF A LIQUID MEDIUM UPON THE SURFACE OF SAID SUBSTRATE A COATINGFORMED FROM A MIXTURE OF BETWEEN 30%-5% BY WEIGHT OF AT LEAST ONELAMINATED METALLIC LUBRICATING AGENT SELECTED FROM THE CLASS CONSISTINGOF SULFIDES AND DISULFIDES OF MOLYBDENUM, TUNGSTEN, TITANIUM AND URANIUMAND BETWEEN 70%-95% BY WEIGHT OF AT LEAST ONE REDUCIBLE METALLICCOMPOUND OTHER THAN SAID METALLIC LUBRICATING AGENT SELECTED FROM THECLASS CONSISTING OF SULFIDES AND DISULFIDES, SAID COMPOUNBD BEINGREDUCIBLE TO FORM A METALLIC MATRIX BONDED TO SAID METAL SUBSTRATE AT ATEMPERATURE AT WHICH THE METALLIC LUBRICATING AGENT DOES NOT UNDERGOSUBSTANTIAL REDUCTION; AND HEATING SAID COATED METAL SUBSTRATE IN AREDUCING ATMOSPHERE AT A TEMPERATURE HIGH ENOUGH TO REDUCE SAID METALLICCOMPOUND TO THE METAL BUT BELOW THE TEMPERATURE AT WHICH SUBSTANTIALDECOMPOSITION OF SAID LUBRUCATING AGENT TAKES PLACE UNTIL SAID METALLICPOUND IS REDUCED TO METAL THEREBY TO FORM A METALLIC MATRIX WHICH ISBONDED TO SAID SURFACE OF SAID METAL SUBSTRATE AND WHICH ENTRAPS ANDBONDS SAID SOLID LUBRICANT TO SAID SUBSTRATE.